Noise interference on VHF caused by plotter.

[sharpness]

I've found when the plotter/radar (RL70C) is on it causes constant noise interference to the VHF (Icom 411) which is located near to it. I'm fairly certain there isn't an earth/ground fitted to the VHF which i understand can help eliminate this problem, but before i start taking half the boat apart to run a cable, i thought i would ask if there are any other suggestions anyone had, or indeed if you agreed with the ground cable idea ?

Thank you in advance for any replies.

 

[rob2]

I'd start by making sure the cables for the radar don't run in the same bundle as the VHF's. Radar can be remarkably broad spectrum and induce interference into other systems - anyone who has driven into Heathrow will know that their ground radar obliterates FM in your car!

Rob.

 

[David2452]

When you say "near" is it outside the safe install distance spec for both units as in the install manuals? I doubt a ground will eliminate the problem. Assuming they are far enough apart, the first thing as suggested above is to check cable proximity and wave a hand held close to see is the RFI is radiated or conducted. You may have some success by installing a ferrite in the supply line close to each unit too, particularly if the RFI is conducted.

 

[lenseman]

I've found when the plotter/radar (RL70C) is on it causes constant noise interference to the VHF (Icom 411) which is located near to it. I'm fairly certain there isn't an earth/ground fitted to the VHF which i understand can help eliminate this problem, but before i start taking half the boat apart to run a cable, i thought i would ask if there are any other suggestions anyone had, or indeed if you agreed with the ground cable idea ?

Thank you in advance for any replies.

This is my specialism. You haven't actually stated whether the interference is on all channels or just specific ones?

First you have to work out how the interferer is getting inside your Icom. These are the three methods:

1) In via the DC supply to the VHF radio

2) In via the VHF antenna.

3) In via the case (directly onto the PCB and components). This is the least likely route but has been known.

Firstly, the most probable route, disconnect the VHF antenna. Do you still get interference in the Icom?

If you do, try connecting the VHF radio to an independent DC battery (Engine battery if separate from the domestic supply)?

You also might find that the Raymarine RL70C is only causing interference under certain conditions, doing certain tasks or at specific ranges or screen brightness?

Get back to me if I can assist further?



.

 

[sharpness]

Thank you all for the above replies. Gives me some starter points to try this weekend, and I will post a reply on Sunday night with what I find, or more likely having more questions to ask you all. Your help is much appreciated.

 

[sharpness]

Managed to try a few of the above suggestions today before the british summer (rain) took charge.

- I found the Interference noise on the VHF was only happening on the channels 64 up to 88. For the lower numbered channels including 16 there was no interference.

- Disconnecting the VHF aerial stopped the interference on these channels, feel a bit thick asking this but what does that mean ?

- Holding a handheld VHF in the area of the fixed VHF unit and area beyond also causes interference on the handheld. As per original post the interference only occurs when the plotter/radar RL70c is switched on.

- Checking the VHF it does not have a ground wire fitted. Although i didn't get time to fit one today, i'm not sure in doing so will cure this problem as the handheld VHF has the same symptons ?

- Checking the wiring showed the VHF supply cabling is separate to the plotters.

- Adjusting range, gain and brightness on the radar/plotter didn't have any effect.

If anyone has any suggestions, and particular an explanation as to why the interference stops when the antenna is disconnected i would be very grateful.